A method for attaching a cosmetic body panel to a composite cargo box without inclusion of a conventional integral lip. The cargo box sidewalls are formed without integral lips. A metallic lip member is bonded to the peripheral top rail at the top of the sidewalls, wherein the lip member is configured so as to mimic the surface contour (geometry) of a conventional integral lip, including the slot, notches and wedge shape thereof for like attaching of a cosmetic body panel thereto.